Anemia, a red blood cell disorder, can be grossly defined as a reduction in the ability of blood to transport oxygen. Although red blood cell disorders may be caused by certain drugs and immune system disorders, the majority are caused by genetic defects in the expression of hemoglobin. Disorders of hemoglobin synthesis include deficiencies of globin synthesis such as thalassemia syndromes and structural abnormalities of globin such as sickle cell syndromes and syndromes associated with unstable hemoglobins.
Fetal globin (also known as gamma globin) normally combines with alpha globin chains prenatally to form fetal hemoglobin (HbF). Fetal globin is replaced by beta globin after birth, which then combines with alpha globin to form adult hemoglobin A. Fetal globin performs the same function as beta globin, and can combine with the alpha chains to generate a healthy form of hemoglobin thereby reducing high concentrations of unmatched alpha globin chains.
The various types of beta thalassemias are syndromes resulting from mutations, which produce a deficiency of beta globin chains. In beta thalassemia, the unmatched alpha globin chains aggregate inside red blood cells (RBCs) and their progenitors, causing the premature destruction of RBCs and RBC progenitors, which results in anemia, transfusion-dependence, iron overload, organ failure, and early death.
In sickle cell disease (SCD), one amino acid substitution in the beta globin chain results in the generation of sickling hemoglobin (HbS), which allows polymerization with repeated cycles of deoxygenation. Polymerization results in “sickling” of RBCs. The sickled RBCs undergo hemolysis, while adhesive sickled RBCs occlude the microcirculation, provoking widespread tissue ischemia and organ infarction. The natural history of SCD is marked by painful crises, acute chest syndrome, and eventual potentially life-threatening sequelae, including renal insufficiency, retinitis, osteonecrosis, osteomyelitis, aplastic crises, functional asplenism, stroke, priapism, and severe pulmonary hypertension.
The disclosure herein provides novel methods and compositions for raising fetal hemoglobin in a patient with a blood disorder, including beta thalassemias and sickle cell disease.